Video Random Access Unit Types for Flexible Stream Switching
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Solution Overview
Problem
Existing video encoding standards limit the flexibility of random access points in video bitstreams, restricting the ability to perform operations like fast forwarding, rewinding, and seamless switching between video streams due to constraints on decodable leading pictures.
Innovation Solution
Introduce 'clean random access' (CRA) and 'broken link access' (BLA) pictures that allow non-decodable leading pictures after CRA pictures, using flags or indicators to manage these pictures, and redefine unit types and constraints to simplify mapping to container formats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constraints on decodable leading pictures are maintained in existing video encoding standards, then decoding reliability is improved, but flexibility of random access points and adaptability of video delivery are reduced
Solution Approach 1:
The patent segments the bitstream into distinct access unit types (CRA access units, BLA access units, IDR access units) with different decoding characteristics. This segmentation allows the system to provide multiple random access point types, each suited for different operational requirements, thereby improving both reliability and adaptability simultaneously.
Solution Approach 2:
The patent introduces new parameters and flags (e.g., broken_link_flag, random_access_skipped_leading_picture_flag) that control the decoding behavior of leading pictures. By changing these parameters dynamically, the system can adapt the decoding process to different scenarios, resolving the contradiction between maintaining reliability and providing flexibility.
2Adaptability or versatility
If non-decodable leading pictures are allowed after CRA pictures to increase access points, then adaptability of video delivery is improved, but complexity of decoding operations increases
Solution Approach 1:
The patent makes the decoding process dynamic by introducing flags that indicate whether leading pictures should be decoded or skipped. The decoder adapts its behavior based on these flags, allowing non-decodable leading pictures to be handled gracefully without requiring complex error recovery mechanisms, thus improving adaptability while controlling complexity.
Solution Approach 2:
The patent treats certain leading pictures as disposable when they cannot be decoded, using them only when decodable and discarding them when not. This approach allows the system to attempt flexible random access without investing in complex error correction, resolving the contradiction between adaptability and complexity.
3Productivity
If mid-bitstream CRA pictures are allowed with non-decodable leading pictures, then productivity of video editing operations is improved, but difficulty of detecting and measuring decoding state increases
Solution Approach 1:
The patent uses distinct flags and markers (analogous to color changes) to indicate the decoding state of pictures. The random_access_skipped_leading_picture_flag and other indicators provide clear, easily detectable signals about whether leading pictures were decoded or skipped, making it simple for editing operations to detect the decoding state without complex analysis.
Solution Approach 2:
The bitstream structure is designed to be self-describing, with embedded flags that automatically indicate the decoding status of each access unit. This self-service approach allows editing operations to quickly determine decoding state without external information, improving productivity while keeping detection simple.
Data Source
AI summary
Disclosed herein are innovations for bitstreams having clean random access (CRA) pictures and/or other types of random access point (RAP) pictures. New type definitions and strategic constraints on types of RAP pictures can simplify mapping of units of elementary video stream data to a container format. Such innovations can help improve the ability for video coding systems to more flexibly perform adaptive video delivery, production editing, commercial insertion, and the like.